The reason most children receive MMR+V is because it is superior to a single shot based on past data. MMRV received Food and Drug Administration approval in 2005, but a few years later, it was found that the risk of febrile seizures increased slightly when given to children 12 to 15 months of age as the first of two doses (the risk was not increased for the second recommended dose, given at 4 to 6 years of age).
The increase is modest — there were 7 to 8.5 seizures per 10,000 first doses of MMRV vaccine, compared with 3.2 to 4.2 per 10,000 first doses of MMR + V vaccine, the analysis found. This difference results in an additional febrile seizure for 2,300 to 2,600 children. Febrile seizures are generally harmless—however frightening it may be for a parent to observe. A febrile seizure is simply a seizure associated with a fever, and they can be triggered by almost anything that can cause a fever, such as the flu or an ear infection. In almost all cases, children make a full recovery with no long-term effects. By the age of 5, about 5 percent of all children have experienced a febrile seizure for one reason or another.
Again, given the comparative increase over MMR+V, ACIP in 2009 reviewed the data from that period and decided that MMR+V was preferred over MMRV. However, MMRV was still considered safe and effective and remained an option for parents in consultation with their doctors. Since then, no new information has changed this opinion among experts.
Sensitive babies
Between 2015 and 2025, the use of MMRV among children in King County remained stable at 15 percent over the decade, despite rated recommendations. And that 15 percent had clear demographic characteristics: Children who received MMRV as their first dose were more likely to be from minority racial and ethnic groups than other vaccinated children. By comparison, significantly more of them received a “catch-up dose” after the initial window of 12 to 15 months, instead of between 16 and 47 months. Children who received MMRV were more than three times more likely than other vaccinated children to qualify for a federal program that offers free vaccines to children from low-income families. They were nearly four times more likely to be vaccinated at a clinic with a safety net.
